The present invention generally relates to modem units, and more particularly to a modem unit which is provided with advantageous functions of both data communication and facsimile communication.
Recently, when using a modem card with a personal computer such as a portable or lap-top personal computer, it has become possible to utilize both the facsimile communication function and the data communication function. The modem card is also sometimes referred to as a communication card.
On the other hand, the standards for the Group III facsimile machines are prescribed under CCITT Recommendations T4, T30, V21, V27ter, V29. The standards for the data communication are prescribed under MNP-4, 5 CCITT V22, V22bis, V42, V42bis.
FIG. 1 shows an example of a conventional modem card. A modem card 50 shown in FIG. 1 uses microchannels as an interface between the modem card 50 and a personal computer which serves as a host. The modem card 50 includes various kinds of peripheral large scale integrated circuits (LSIs) which are coupled to a CPU bus, and controls the Group III facsimile communication function by firmware. As the modem function, the modem card 50 is provided with only the Group III facsimile modem V21, V27ter, V29.
In FIG. 1, a CPU 101 is made up of a chip model 80C186, for example, and controls each of the blocks shown in FIG. 1 and controls the facsimile procedure. A bus driver 102 is made up of a chip model TE7730, for example, and couples address and data buses of the CPU 101 to a local bus 118. A programmable array logic 103 is coupled to the bus driver 102, and carries out decoding of the address and forming of an input/output control signal based on a control signal from the CPU 101. A read only memory (ROM) 104 stores program codes for controlling the CPU 101, and a dynamic random access memory (DRAM) 105 is used as a work memory for temporarily storing data for control.
A bus driver 106 is made up of a chip TE7730, for example, and couples the data bus to a codec 107. The codec 107 is made up of a chip model HPD72185, for example, and carries out compression and expansion, that is, coding and decoding, of the image data. A multi protocol sequence controller 108 controls the communication sequence. A modem 109 carries out modulation and demodulation in conformance with the facsimile procedure (V21, V27ter., V29). A network control unit 110 controls the line.
A DTMF receiver 111 is made up of a chip model MSM6893, for example, and receives the DTMF signal. An input/output port controller 112 controls the input/output ports. A voice synthesis circuit 113 is made up of a chip model MSM6258, for example, and carries out an ADPCM voice synthesis. The voice synthesis circuit 113 also has recording and reproducing functions. Bus drivers 114 and 115 are respectively made up of a chip model TE7730, for example, and provide an interface between a microchannel bus 119 and the local bus 118. A bus controller 116 is made up of a gate array, and controls the microchannel interface. A gate 117 is provided for interrupt purposes.
FIG. 2 shows another example of the conventional modem card. A modem card 50A shown in FIG. 2 is coupled to a personal computer 51 via a serial interface 52.
However, conventional modem cards require a relatively long communication time. For this reason, there are demands to reduce the required communication time of the modem card. More particularly, there are demands to realize a modem unit in which the communication time of the Group III facsimile communication is shortened and the communication of high quality text data is made possible.